How turning manure into plastic could economize one type of energy production

Dairy is a big industry in Idaho. That brings certain byproducts, including manure. Lots of manure.

While pursuing his PhD, University of Idaho civil engineering professor Erik Coats became interested in resource recovery, particularly when it comes to plastic. It turned out that pursuit dovetailed very nicely with Idaho’s wealth of manure.

“(University of) Idaho is a land grant university. Part of the land grant mission is to respond to the needs of the constituent industries and otherwise in your state,” Coats said. “I’m doing this bioplastics research. To make bioplastics, I need a lot of carbon. I need a lot of electrons. Well, they’re in manure. It works out perfectly.”

Coats’ team has now developed a process that uses bacteria to turn manure into biodegradable plastic. It can be used to create printer cartridges or plant pots that disintegrate after use.

“You go down to the nursery, you buy a large tree or a large shrub,” Coats said. “In this case, you would just plant the plant and the pot together and the bacteria would consume plastic pot.”

Coats believes his team can commercialize the technology within five years. Right now, they are working with scale models of the large tanks the process would require. Their small tanks can produce two to five pounds of plastic a day.

The process starts with placing manure in a tank, where it ferments. The manure separates into liquids and solids.

Civil engineering professor Erik Coats and PhD student Nick Guho work with a scale model of a tank that converts manure into biodegradable plastic. The tank can produce two to five pounds of plastic a day. Photo courtesy of University of Idaho

The liquids are removed from the tank and fed to bacteria. The bacteria process it and store it in their body, much like how humans store fat. Once the bacteria are fattened up, the team kills them with chlorine and dries them.

The raw plastic can be incorporated into products like the planter pot or matting used for erosion control. Otherwise, it can be purified to be used for a product like a printer cartridge.

The solids can be fed into a manure digester, which create electricity from methane. Coats said it makes sense to pair the two systems together.

“The economics [of a digester are] very tenuous. It’s difficult to be profitable given low electricity prices, particularly here in the northwest,” Coats said. “Our idea is to plug in our plastic technology to digesters and add another commodity so we can improve the economic bottom line of these systems.”